Hydrochloric Acid Corrosion

General Information

Hydrochloric acid finds widespread use across various industries, serving as a crucial component in chemical manufacturing, food production, pharmaceuticals, rubber manufacturing, metal cleaning, and well activation (acidizing), among others. In the refining industry, HCl typically emerges as a by-product during the decomposition reactions of both inorganic and organic chlorides in the crude distillation process, impacting the integrity of the overhead (OVHD) section of the atmospheric distillation tower. Additionally, HCl is present in reforming and isomerization units where it either emanates from Cl-containing catalysts or forms during the regeneration of catalysts through the addition of chlorinated compounds. Moreover, HCl is also employed as a bulk chemical, serving as a neutralizing agent in tasks such as water treatment plants or within caustic treatment units.

The Cl- ions in aqueous HCl solutions can penetrate and break down the passive oxide layer of many CRAs (Corrosion-Resistant Alloys), resulting in accelerated corrosion. For instance, UNS S31603 (316L) may corrode at a rate similar to carbon steel under such conditions. Therefore, only a few alloys, such as molybdenum-rich C-276 (UNS N10276) and B-3 (UNS N10675), have demonstrated relatively good resistance — although not complete immunity — to HCl across a wide range of temperatures and concentrations.^{1 2} When using material selection tables for HCl, which are commonly employed in the industry, caution is advised as the data mostly originates from laboratory experiments in controlled environments. The presence of oxidizers like O₂ from the air or ions such as Fe³⁺ or Cu²⁺ may significantly alter the behavior of the alloy.^{3 4}

Choosing resistant materials for HCl is challenging, so the practice of lining internal steel pipelines/vessels with polymeric materials has become a popular strategy to reduce bulk HCl corrosion in specific regions.^{5 6} This method is effective but demands highly skilled personnel for assembly, maintenance, and inspection of internally lined systems. Table 1 outlines typical areas susceptible to HCl corrosion.

Table 1 Potential locations for HCl corrosion in process units.⁷

Hydrochloric Acid Corrosion is governed by a combination of several factors like chemical species and concentration, temperature, materials and/or flow regimes.

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Tools

Below are our user-friendly calculators and integrity tools to estimate the HCl corrosion of carbon steel and some CRAs.

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HCl-Corrology®

HCl-Corrology® is designed to provide rapid corrosion rate estimates for steels and Corrosion Resistant Alloys (CRAs) in hydrochloric acid service. It allows you to evaluate the impact of key process parameters like acid concentration and temperature, on corrosion rates.

Note: Calculation results are currently hidden. Register for Free Trial to unlock Corrosion Rate and Service Life Results.

Integrity Risk Indicator (Corrology®-IRI: HCl)

The Challenge: Moving Beyond Linear Estimates

In aggressive HCl environments, traditional linear corrosion tracking often misses the “safety precipice”. As wall thickness decreases, risk does not grow steadily - it accelerates exponentially. Relying on basic calculations can lead to either premature equipment replacement or, worse, unexpected failure.

The Solution: The HCl Integrity Risk Indicator (IRI-HCl)

The IRI-HCl quantifies asset risk by calculating corrosion rates, service-life context, and empirical remaining-life indicators through a margin-aware, API 581-inspired engine. This tool functions as a sensitivity analysis engine, allowing you to evaluate how shifting process variables impact different alloys in Predictive Mode to determine the most robust material for your specific operating window.

The Advantage

Access high-fidelity modeling features designed for defensible engineering decisions:

• Non-Linear Risk Scaling: Utilize a logarithmic-exponential transformation that reflects the true physical reality of risk escalation in late-life degradation states.

• Dynamic Inspection Credit: Input your Inspection Effectiveness (Class A–E) to see how high-quality data reduces uncertainty and optimizes maintenance intervals.

• Auto-Derived Prior Confidence: Prior confidence is automatically computed from the uninspected time interval (t_uncertainty): <3 years → High, 3–5 years → Medium, ≥5 years → Low. This applies in both Predictive and Inspection modes, ensuring API 581-consistent conservatism without manual override.

• Precision Structural Floors: Take control of your model by setting Manual T-Min structural floors to match your equipment’s unique geometry.

• Expert Calibration: Gain confidence with a model structured against a 6-point lifecycle truth set, ensuring accuracy from low-risk early life to critical thin-wall scenarios.

• API-Aligned Risk Bands: Status and score-pill color are determined by the log probability of failure (log P_f) rather than the 0–100 score scale alone. Thresholds follow API 581 PoF magnitude ranges: log P_f ≤ −5 → Very Low; −5 < log P_f ≤ −4 → Low Risk; −4 < log P_f ≤ −3 → Moderate; log P_f > −3 → Critical. This ensures that improvements in inspection effectiveness are always reflected in the displayed risk band, even in high-age or thin-wall scenarios where the numerical score is saturated.

Note: The Integrity Risk Indicator (IRI) shown below is a static preview of our Professional+ engine. Register for Professional+ to unlock IRI-HCl tool.

References

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